Light emitting diodes (LEDs) and photo detectors are widely used with or without lenses to facilitate wireless infrared communication in devices such as laptop computers, personal digital assistants, printers, mobile phones, modems, digital pagers, electronic cameras, and hand-held computers. The growing popularity of wireless communication has placed a tremendous demand for small form factor for components such as transceivers within wireless communication devices.
In a typical wireless communication device, an infrared transmitter (e.g. an LED chip/die with lens) is arranged adjacent to an infrared receiver (e.g. a photo detector chip/die) in an arrangement called a transceiver. An embedded LED chip/die with lens is called an emitter. An embedded PD die/chip with lens is called a transmitter. The transmitter and the receiver are connected with an integrated circuit for signal processing. On the surface of the transceiver, there are two lenses. A light emitting diode chip/die is located in or near the center of one of the lenses, and a photo detector chip/die is located in or near the center of the other lens. Conventionally, spherical lenses 110 described by a radius r (115), as depicted in FIG. 1, are employed to ensure proper directional distribution of light.
One method of evaluating LED lenses is the generation of a radiant intensity profile. The radiant intensity profile indicates flux of radiation per steradian of the surface of a lens. The term flux, in this context, refers to the energy per steradian of the emission of the LED. A steradian 210 is a three dimensional unit of spherical geometry, depicted in FIG. 2. One steradian 210 is a solid angle, e.g. a cone that, having its vertex 221 in the center of a sphere 201 of radius r (205), cuts off an area (220) on the surface of the sphere equal to that of a square with sides of length equal to the radius r of the sphere. In other words, one steradian 210 is a solid angle defining an area 220 equal to r2 on the surface of a sphere 201 described by radius r (205).
A radiant intensity profile for a spherical lens is presented in FIG. 3. The curve of flux per steradian in a horizontal direction 310 is substantially symmetrical about the maximum 330. The curve of flux per steradian in a vertical direction 320 is also substantially symmetrical about the maximum 330. This symmetry in both the vertical and horizontal directions is required to satisfy the standards and protocols of the Infrared Data Association (IrDA), a non-profit organization dedicated to developing globally adopted specifications for infrared wireless communication. As can be appreciated, it is desirable for a commercially available device to conform to IrDA standards and protocols.
One approach to meeting the current demand for smaller components within wireless devices is to manufacture smaller spherical lenses for use with LEDs and photo detectors in infrared transceivers. However, as the diameter is decreased for spherical lenses used with LEDs, the brightness of the LEDs decreases, therefore signal output is compromised. As the diameter is decreased on spherical lenses used with photo detectors, less light is received at the photo detector, therefore signal processing is compromised.